1. Field of the Invention
The invention relates to a water separating system for separating water from a water-vapor mixture, having at least one inlet tube disposed on the periphery of a vessel and having an outlet tube for steam provided above the inlet tube.
Such a water separating system having a water separator, which is known, for example, from German Published, Non-Prosecuted Patent Application DE 42 42 144 A1, is usually used in the evaporation system of a once-through or forced once-through steam generator. It serves for separating water from a water/water vapor mixture at the end of a heating surface of the steam generator referred to as an evaporator. It is intended that the system should prevent water from passing into downstream superheater heating surfaces. Such an interference with medium impingement on heating surface inlets leads to different mass flows in the heating surfaces due to heating. The resulting different cooling may lead to impermissible excess temperatures and thus to damage to tubes of the heating surfaces.
The water/water vapor mixture which often flows tangentially into the water separator through conventionally inclined inlet tubes is separated in a vessel by a combination of gravity and centrifugal forces. In the process, the water is separated onto vessel walls and flows downwards, while due to the inclination of the inlet tubes, the steam is initially conducted downwards and, following a flow reversal in the separator, is drawn off in an upper region of the vessel.
However, as the steam content and steam generator loading increase, a cross-section of flow defined by a ratio of downward flow and upward flow becomes narrower, so that the velocities of the mixture components increase and the pressure loss rises. Since water droplets are entrained by the steam due to the comparatively high velocity of the water/water vapor mixture, the separation quality becomes progressively poorer. Furthermore, as the number of inlet tubes increases, the exit conditions of the mixture jet are increasingly impaired.
Published French Patent Application 961 953 has disclosed a water separating system in which a separation apparatus for a partial-stream steam is connected upstream of a vessel on the inlet side.